In one of conventional power supply apparatus used with a DC arc cutter or a DC arc welder, an AC voltage from a commercial voltage source is converted into a DC voltage in a converter, and the DC voltage is applied to an inverter for conversion into a high frequency voltage. The high frequency voltage is, then, voltage-transformed by a transformer, and then rectified and smoothed by a rectifier and a smoothing reactor into a DC voltage. The resulting DC voltage is applied between two output terminals respectively connected to a workpiece to be wrought and to a torch of the DC arc cutter or welder.
A detector detects the voltage appearing between the output terminals. Alternatively, the detector may detect current flowing through either one of the terminals. In accordance with the detected voltage or current, a controller controls the inverter in such a manner that the voltage or the current can be kept constant.
An arc cannot be generated between the torch and a workpiece by applying therebetween the DC voltage alone which is developed through the rectifier and the smoothing reactor. Therefore, an arc initiating circuit is used to initiate an arc between the torch and the workpiece. The arc initiating circuit includes a high frequency generator for generating a high frequency voltage, which is coupled to a primary winding of a coupling transformer to induce a high frequency voltage in a secondary winding of the coupling transformer. The induced high-frequency voltage is applied between the torch and the workpiece via a bypass capacitor, thereby initiating arcing. The arcing is sustained by power supplied through the rectifier and the smoothing reactor.
The smoothing reactor may have large reactance to stabilize the DC voltage to be applied between the output terminals. Such large reactance, however, results in failure to sustain the arcing because it impedes an arc sustaining current flowing from the rectifier through the smoothing reactor.
Power supply apparatus according to the present invention can overcome the problem described above.